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I recently successfully built a 3 lane start using ID and blade sensing circuits that I built myself according to Tnemrap's circuit diagram below.

And here's that circuit diagram made flesh (well, silicon and plastic etc.)!

You can see where the black, red and green wires from the scratch built circuit connect to the Scalextric ID board. The circuit is just 3 resistors, a transistor and the photo sensor. I found an excellent, very small, photo sensor (T2 in the diagram) that fits under the track without fouling the car guide, the QSB363 Subminiature Plastic Silicon Infrared Phototransistor from Fairchild Semiconductor (data sheet.) It's easy to solder to the board and also seems to perform better than the Scalextric SMD ones, being more tolerant of cars with slightly higher ID LEDs (e.g when the braids are holding the car a little too high).

For the blade sensor I used the OPB610 from Optek (data sheet) It's a little tall at just over 8mm, but it seems to work perfectly. The blade sensor circuit isn't really a circuit, its only component is the OPB610! Here it is next to the Scalextric board...

You need to follow RikoRocket's guide above regarding the mods to the Scalextric blade sensor board,

QUOTE "Two new wires from LED to LED crossing over in an X, cut the thin track at the very edge of the board that connects the LEDs together, unsolder the yellow wire from its pad."
Then connect pin 1 of the OPB610 (red wire in the pic above) to the red pad, pin 2 (black) to the black pad, pin 3 (green) to the yellow wire (not the board) and pin 4 (white) to the pad you unsoldered the yellow wire from.

I had trouble working out the track to cut from RikoRocket's pic (remember the LIGHT green parts are the tracks!), so here's a clear pic of that... can also see the white wire from the OPB610 soldered to what was the yellow wire's pad and the X over wires - the thinner red and black wires exiting the picture at top left.

Here it all is, wired up and glued in place (I tested the whole thing with the boards just taped in place before gluing.)
. Make sure the OPB610 slot lines up with the track slot or car guides will hit it

I used half a sensor track from an unused CLC rather than mod a single lane piece for the third lane (after all the CLC only has a sensor on one lane). That way I had the slot for the PB610 and the holes for the QSB363.

Soldering up a circuit from scratch isn't that hard. I did scour the internets to grok the basics. You really must follow the "heat the part(s), not the solder" maxim or you'll just end up with solder all over the board. You can connect the adjacent pins of components by what I call "blobbing over", basically just solder across the two board holes. Also, check the data sheets for the pin-outs of the transistor and slotted optical switch you end up using! Different transistors use different legs for C(ollector), B(ase), E(mitter) (I found this out the hard way). The pin marked with a white dot/dash on a phototransistor corresponds to the arrowed leg in the diagram. See how little I knew before I tried this?

I am now a very happy camper, mucho respect to Tnemrap and RikoRocket! If I can do this, you can too!

Here's a list of the components I used with cost in US dollars:

CODE1 x OPB610 Slotted Optical Switch $1.69
1 x QSB363 Infrared Phototransistor $0.25
1 x BC33725 Small Signal Transistor $0.16
2 x 286-2.2K-RC 2.2K Small Metal Oxide Resistor $0.49
1 x 286-4.7K-RC 4.7K Small Metal Oxide Resistor $0.49

Total $3.08

A bit cheaper than chopping up a 6 car PB, eh?
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